Metal-oxide-metal (MOM) capacitors are frequently formed during the manufacture of complementary metal oxide semiconductor (CMOS) devices. One who is skilled in the art is readily aware that a capacitor comprises two conductive surfaces separated by a dielectric. In semiconductor manufacture, MOM capacitors in CMOS devices are commonly formed on a silicon substrate by depositing a first metal layer of titanium (Ti), followed by a titanium nitride (TiN) barrier layer. Typically, silane-based oxide is deposited to form the dielectric. The oxide layer is then deposited, masked and etched. In those areas where MOM capacitors are not required, the oxide is etched away and down to the TiN barrier layer. During the removal of the photoresist layer defining the MOM capacitor, a portion of the TiN barrier oxidizes, which requires a deglaze (oxide removal) step prior to deposition of the top metal plate. Finally, the second metal layer, which may be aluminum (Al), copper (Cu), or aluminum copper alloy, such as AlCu(Si), is deposited to form the MOM capacitor.
A problem arises, however, during the oxide deglaze process in that the deglaze chemistry attacks the oxidized TiN barrier layer where it has been exposed. This causes the TiN barrier layer to erode in those exposed areas. The erosion of TiN material may be as much as 10 nm to 50 nm. The conventional solution to this problem has been to deposit a thicker TiN layer in order to compensate for this corrosive loss. However, a thicker metal/nitride layer increases the overall sheet resistance of the metal stack--an undesirable side effect. An additional problem results from this TiN layer erosion in that when the TiN layer is attacked, the silicon dopants, such as boron, phosphorus and arsenic, and titanium itself may diffuse through the eroded TiN barrier and into the upper or top metal layer. This diffusion can result in junction spiking. All of these problems result in reduced die yield, and increased manufacturing costs.
Additionally, while the titanium layer acts as a good adherent, it does, however, affect the subsequent grain size of the aluminum, aluminum/copper or aluminum/copper/silicon electrode layers of the contact plug. This, in turn, can reduce the conductivity of the aluminum stack layer.
Accordingly, what is needed in the art is a barrier material for MOM capacitors that addresses the deficiencies of the prior art.